Corrosion resistant article and methods of making

Abstract

An article and method of forming the article are disclosed. The article has a surface comprising a duplex nanostructured ferritic alloy. The surface includes a plurality of nanofeatures that include complex oxides of yttrium and titanium disposed in an iron-bearing alloy matrix. The iron-bearing alloy matrix includes both a ferrite phase and an austenite phase. Further, a concentration of a chi phase or a sigma phase in the duplex nanostructured ferritic alloy at the surface is less than about 5 volume percent. The method generally includes the steps of milling, thermo-mechanically consolidating, annealing, and then cooling at a rate that hinders the formation of chi and sigma phases in the duplex nanostructured ferritic alloy at the surface.

Description

BACKGROUND[0001]The invention relates generally to a nanostructured ferritic alloy comprising a duplex microstructure (referred to as the duplex NFA) and articles made of such alloys. More particularly, the invention relates to an article having a duplex nanostructured ferritic alloy surface with good corrosion resistance, and methods of forming the article.[0002]Material selection is especially important in equipment components used in sour and acid environments commonly associated with oil and gas extraction installations. Sour gas wells may contain carbon dioxide, chlorides, hydrogen sulfides, and free sulfur, and may operate at temperatures up to 400° C. This type of corrosive environment requires carefully designed alloys to enable components to maintain their structural integrity over their service life.[0003]Conventional corrosion resistant steels include ferritic, austenitic, and ferritic / austenitic duplex steels. In general, ferritic steels have improved stress corrosion cr...

AI Technical Summary

Benefits of technology

[0005]One embodiment of the invention is directed to an article. The article has a surface, and this surface includes a duplex nanostructured ferritic alloy. The alloy includes a plurality of nanofeatures disposed in an iron-bearing alloy matrix; this plurality includes complex oxide particles that include yttrium, titanium, and optionally other elements. The iron-bearing alloy matrix includes both a ferrite phase and an austenite phase. Further, a concentration of a chi phase or a sigma phase in the duplex nanostructured ferritic alloy disposed at the surface is less than about 5 volume percent.

Problems solved by technology

In general, ferritic steels have improved stress corrosion cracking resistance in chloride-containing environments, but the strength is relatively low.

Austenitic and duplex steels have good corrosion resistance, low to intermediate strength, but inferior stress corrosion cracking resistance.

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